1. Field of the Invention
The present invention relates to a bearing device, more particularly to a tapered-land thrust bearing device.
2. Description of the Prior Art
A well-known conventional tapered-land thrust bearing comprises a flat disk-shaped bearing member, with tapered surfaces and flat-land surface successively on the bearing surface in the peripheral direction thereof or with oil grooves formed in a part of the tapered surface. Such a conventionally known tapered-land thrust bearing is made, for example, of cold rolled carbon steel (SPCC), according to G3141 of Japanese Industrial Standard, hereinafter referred to simply as "JIS", subjected to nitriding treatment for a bearing surface hardness of 450 to 500 Hv (Vickers' hardness).
Such a tapered-land thrust bearing is used, for example, in an automotive transmission. The rotating shaft or other member used together with the bearing, however, is generally machined relatively roughly. The rough contact surface of the shaft, etc., has an adverse effect on the performance of the tapered-land thrust bearing, decreasing the bearing load capacity, creating large frictional force upon startup, breaking the oil film and causing abrasive wear, and causing bearing seizure. These problem can be prevented by increasing the machining precision accuracy of the shaft, etc., however, this would entail considerable cost and is therefore not feasible in practice.